This invention relates to electromagnetic projectile launchers and, more particularly, to such launchers that include a switching device which provides for a rapid repetition rate for successive launches.
Electromagnetic projectile launchers are capable of accelerating various types of projectiles to high velocities. Several possible applications of electromagnetic launchers, such as fusion reactor pellet injection, impact fusion and weapons, require that the launcher accelerate a projectile to very high velocities and have a rapid repetition rate for successive shots.
Electromagnetic projectile launchers are known which comprise a pair of generally parallel conductive rails, a sliding conductive armature between the rails, a source of high current, and a switch for commutating this current into the rails and through the armature. Current flowing in the armature produces a force which accelerates a projectile along the projectile rails. Several different projectile configurations have been proposed, however, the projectiles are usually provided with a metallic armature or a plasma armature. The metallic armature projectile has a conducting member on its base which conducts current from one projectile rail to the other by using a sliding contact. These armatures are generally made of a flexible, brush-type conducting material which is forced against the projectile rails by electromagnetic forces which ultimately propel the projectile. The plasma armature projectile utilizes an electric arc for the conduction path. By providing a tight seal between the projectile and bore, the plasma cannot blow pass the projectile and therefore transfers the electromagnetic forces acting on it to the projectile. Plasma drive offers the advantage of being very low in mass, so that substantially all of the energy for acceleration goes into the launcher payload. However, a slow moving plasma can cause rail damage during the initial stage of projectile acceleration. The present invention concerns a novel switch for commutating the high current into the projectile launching rails. This switch allows for a high repetition rate and rapid projectile reloading. It also imparts an initial velocity to the projectile.
Several configurations for the commutating switch have been proposed where the switch performs the functions of conducting current during an initial charging sequence and commutating current into the projectile rails during the firing sequence. These schemes have consisted primarily of a switching armature which conducts current during the charging sequence and then is propelled using electromagnetic forces across an insulating surface to commutate current into the projectile rails and the projectile armature. Switching armature schemes generally incorporate a shock absorber system to allow recovery of the switching armature. Switching armatures have been proposed for use in launchers which utilize both a metallic armature and a plasma armature. The switching armature scheme relies on rapid movement of the switch to commutate current into the armature and reloading of the launcher must be accomplished before another launch is initiated. In addition, repeated usage of the switching armature will result in armature deterioration from the effect of the commutating arc.
A rotary type commutating switch has been proposed to allow for an increased repetition rate. Various geometries of insulating and conducting sections of a rotating wheel which contact stationary current collecting members have been proposed. Rotation of the wheel switches current from the stationary current collecting members to the projectile rails.
Regardless of the type of commutating switch used, severe rail damage can occur during the initial acceleration of a projectile in the launcher bore. This damage can be reduced to manageable levels by proper projectile armature design and by imparting the projectile with an initial velocity which is high enough to reduce the energy density on the rails in the breech of the launcher.
Neither the switching armature nor the rotary switch provides a method of firing an electromagnetic launcher at high repetition rates for sustained periods. Rapid fire capabilities require that a method be devised for rapidly loading the projectile, imparting an initial velocity to the projectile, rapidly commutating current to the rails and initiating a plasma drive if needed. In addition, the switch must be such that sustained firing will not degrade it.